This blotter uses the same image as a note pad that I worried might be a replica, and the blotter also has a string of tiny numbers and “Printed in U.S.A.” at the bottom. Yet I feel pretty confident that the blotter is not a replica.
For one thing, I’ve seen similar numbers on blotters that are obviously old and used. For another, few people use fountain pens nowadays, so while blotter paper is still made, it is rare and I can’t see a rail fan buying some to make forgeries of old blotters. I could be wrong about the note pad sheets, but I feel comfortable that this blotter is authentic.